Radiation therapy is an important modality for the treatment of cancers. Limitations to this treatment include local failure due to adverse cellular, tumor or host factors. An important basic consideration in tumor control is the intrinsic radiation sensitivity or resistance of the cells forming the tumor. Poly(ADP-ribose) polymerase (PADPRP) is a nuclear enzyme that requires DNA for activity and whose catalytic activity is correlated directly to the number of strand breaks, both in vitro and in -vivo. It has been shown that poly(ADP-ribosylation) of chromatin-associated proteins occurs during biological reactions involving DNA strand breaks, including the repair of damage induced by ionizing radiation. Contrary to expectations, our previous studies have demonstrated that some radiation sensitive tumor cells (i.e., Ewing's sarcoma (ES)) express a consistently higher steady state level of MRNA transcript and higher enzyme titers for the polymerase than radiation resistant cell lines. We propose to study the comparative roles of poly(ADP-ribose) metabolism in relation to radiation damage in human radiation sensitive cells and radiation resistant cells. The stability of the mRNA and the turnover of the gene product will be studied in response to radiation damage. In addition, using,antisense oligonucleotides, we will investigate the effects of modulation of this enzyme on radiation survival, repair of DNA strand breaks, and cell cycle kinetics in sensitive and resistant cells. We will be especially concerned with the role of ADP-ribosylation on G2 arrest, using specific antibodies to cell cycle regulatory proteins and to the polymer by 2-D protein gel electrophoresis analysis. The data obtained from these experiments will help determine molecular events associated with cellular response to ionizing radiation. Understanding the mechanisms of radiation sensitivity and resistance of tumor cells offers the opportunity to develop strategies for improving the clinical therapeutic ratio.